1. Field of the Invention
The present invention relates to way of structuring input/output plugs and a digital interface for equipment in a communications system where a number of items of equipment capable of mixing and transferring as packets control signals and information signals are connected via a bus.
2. Description of the Related Art
In conventional communication systems where AV equipment such as, for example, Video Tape Recorders (hereinafter referred to as VTRs), Televisions (hereinafter referred to as TVs) etc. are connected together via analog AV signal lines and digital control signal lines, a DDB (Domestic Digital Bus) has been used. Examples of this kind of system are described in the European patents belonging to the same applicant relating to this kind of communications system. These patents are publication number EP 0 604 166, EP 0 610 630, EP 0 604 167 and EP 0 608 624. Applications are currently under way for American patents which will correspond to these patents.
First, a description will be given of an example of this kind of communications system with reference to FIG. 17. This kind of communications system is equipped with a TV, a VTR 1, a VTR 2, a Multi Disc Player (herinafter referred to as an MDP), and an editor. The VTR 2 is also connected to a device which is not compatible with a digital control signal line (hereinafter referred to as a non-bus compatible device).
The AV signal input/output plug for the non-bus compatible device is connected to input/output plugs of other devices only by plugs described by P1, P2 and P3, protruding directly out from units known as switchboxes (SW box) via analog AV signal lines. Commands such as connection control commands etc. are sent and received by other devices via analog AV signal lines and digital control signal lines which are connected separately. Each item of equipment is also equipped with one or more functional units, which in the case of a VTR would be a deck for recording and playing back and a tuner for selecting the signal to be received, and in the case of a TV, would be a monitor and an amplifier. There is also an AVC (AV controller) for controlling the operation of all of the items of equipment, although this is not shown in the diagrams. In the following, these functional units may also be referred to as sub-devices.
Control connection can be carried out in two ways in a communications system structured in this way. These ways, which will be referred to as connection control method 1 and connection control method 2, will be described in numerical order.
In connection control method 1, information pertaining to the connection structure for each device, i.e. which plug is connected to which plug of an opposing item of equipment and whether plugs are used for input or output, is pre-stored by the user. In this way, an output plug which it is considered will make a connection from the sub-device which is to be the AV signal source to the destination may be selected as required while the item of equipment is receiving the connection control command. Alternatively, a path may be set up within the device between the input plug of the designated number and the appropriate output plug, with a command then being transmitted to the device connected previously to the output plug. The object is then achieved at the point in time when the command reaches the sub-device within the specific device indicated by the destination. At this time, commands cannot be transmitted via the control signal line when the device is a non-bus compatible device. The plug numbers for devices connected to this kind of device therefore have to be directly specified (for example, in the case in FIG. 17, the input plug P1 for the VTR 2 is directly specified).
The following is a description with reference to FIG. 18 of the sequence in connection control method 1 when an MDP output is recorded on a VTR 2 as a result of instructions from an editor. FIG. 18(a) shows the communications sequence and FIG. 18(b) shows the commands.
First, the MDP receives a command giving an instruction to connect the deck output to the deck of the VTR 2 from the command master (editor) (communication 1). At this time, none of the output plugs of the MDP are connected to the VTR 2. However, the output plug P3 is connected to the input plug P1 of the VTR 2, so a command is therefore sent to the VTR 1 via a path from the input plug P1 to the switchbox (communication 2).
When the VTR 1 receives this command, none of the output plugs are connected to the VTR 2 but the output plug P3 is connected to the input plug P1 of the TV. A command is therefore sent via a path from the input plug P1 via the switchbox to the TV (communication 3).
When the TV receives this command, it is understood that the output plug P3 is connected to the input plug P2 of the VTR 2 and a command is sent to the VTR 2 form the input plug P2 via the deck (communication 4).
The VTR 2 then receives this command and changes over the switchbox connection so as to input from the input plug P2 to the deck. Once the VTR 2 completes the process 4, the TV is notified of this completion. Upon receival of this, the TV gives notification to the VTR 1 that the process 3 is completed. When the VTR 1 then receives this, it gives notice to the MDP that the process 2 has been completed. Upon receiving this, the MDP gives notice to the command master that the process is completed. These packets are omitted from the diagrams.
Here, an editor has been set up as the command master. However, rather than setting an editor up on the communications system, a structure may be adopted where the MDP and the VTR have command master functions.
In a second connection control method, a single central item of equipment (in the following, this is an AV center) manages all of the connection information regarding which kinds of equipment are connected together via which numbered ports in which directions. If a command requesting AV signal connection via the digital control signal line is then received, this command is sent via the digital control signal line to the target device. The target device then receives this command and changes over the input/output. At this time, it is possible to designate the sub-device by category via the initial connection request from the command master (by BS, CS etc. which are more in line with the objectives, rather than by a tuner etc.). However, at the time of a connection request, an item is only aware of its own plug structure.
The following is a description with reference to FIG. 19 of the sequence in a connection control method 2 when a TV is taken as an AV center and output from an MDP is recorded by a VTR 2. Here, FIG. 19(a) shows the communications sequence and FIG. 19(b) shows the commands.
First, the TV receives a command from the command master instructing it to connect the MDP deck output to the deck of the VTR 2 (communication 1). The TV then receives this command and sends a command to the MDP to the effect that the output for the deck sub-device is to be outputted from the output plug P3 (communication 2).
If the MDP receives this command, the switchbox is changed over so that the deck output is connected to the output plug P3 and notification of the completion of the changeover process is then sent to the TV. If the TV then receives this information, a command is sent from the input plug P1 via the output plug P3 to the VTR 1 (communication 3).
If the VTR 1 receives this command, the switchbox is changed over so that a connection is made from the input plug P1 to the output plug P3 and notification of completion of the changeover process is sent to the TV. If the TV then receives this notification, a command is sent from the input plug P2 to the deck to be inputted to the VTR 2 (communication 4).
Providing the VTR 2 receives this command, the switchbox is changed over so as to input from the input plug P2 to the deck. The TV is then notified when the changeover process is complete.
If the TV then receives notification of completion from the VTR 2, notification of completion of the connection is sent to the command master.
However, with connection control method 1, the digital control signal line becomes confused as a result of commands being transmitted between items of equipment which neighbor each other. It is also possible that an infinite loop may be formed depending on the settings of items of equipment in the connection line. It is also necessary to know the structure of the items of equipment which it is intended to control with the command master and the structure of the connections between the equipment in the overall system, so the plug numbers can be designated directly.
Also, in connection control method 2, no matter how simply a connection is made between a plug for an item of equipment and the preceding item of equipment to which the plug is connected, this cannot be achieved without a request being made to the AV center. Further, designation can be made using the sub-device category at the time of a connection request, but plug set-up can only be achieved for an item of equipment's own plugs, for which the structure is known.
It is therefore apparent that connection control of a variety of AV signals by holding connection information for input/output plugs on the outside of items of equipment and present within interfaces is not appropriate. It is therefore the object of the present invention to provide a communications system capable of resolving these kinds of problems.